1. Field of the Invention
This invention relates broadly to apparatus and methods for underwater optical recording. More particularly, it concerns improvements in such apparatus and methods that activate the system when a photographic subject is in the camera's field of view and the distance to the subject is suitable for in-focus photography.
2. Description of the Prior Art
A great number of underwater photographs are taken with cameras which have limited remote controls. This is particularly true of deep-sea 35 mm. camera systems where camera lens opening and focus are preset and the photographer must somehow arrange for the subject to be at the correct distance and within the field of view at the time of exposure.
One approach to providing better control in underwater photography would be to incorporate the ranging features of advanced, above surface cameras. Such cameras use a variety of tehniques to obtain proper exposure conditions for control. The most common is a triangulation arrangement which superimposes the images received by a pair of spaced optical receivers and provides automatic, mechanical adjustment of the lens until the received images are coincident. Microelectronics are used to perform the image comparison and thereby provide automatic focusing (see U.S. Pat. Nos. 3,435,744 & 4,313,654).
Other advanced surface cameras use microprocessor based optical-image analyzers to determine correct focus. Also, sonar systems are used in some cameras. The optical systems of the surface cameras generally use infrared light beams with reflected light intensity, image analysis and triangulation. Unfortunately, the devices and techniques developed for surface cameras are not directly transferable to underwater camera systems. Differences between the physical properties of air and water result in major differences in the propagation of light and sound in the two media. Additionally, spurious material and signals can cause many "false" exposures to occur with underwater photography while this is not a serious consideration in use of surface cameras. Therefore, a camera system which depends on the propagation of energy waves for operation must be designed for the medium in which it is to be used. Extensive development work has occurred relative to underwater photography. Such work has included use of (a) optical triggering of underwater cameras, e.g. , see U.S. Pat. No. 3,446,555 and (b) sonar techniques, e.g., see U.S. Pat Nos .4,105,990; 4,335,944; 4,381,144 and 4,447,896.
Notwithstanding the extensive prior work and developments with surface and underwater camera systems, substantial improvements are needed for the underwater systems, e.g., to provide for (1) more efficient use of battery or other power, (2) saving of film and (3) mitigation of triggering of exposure by spurious materials or events. My prior invention disclosed in U.S. Pat No. 4,707,094, the contents of which are incorporated herein by reference, provided such improvements by automatic triggering of unattended underwater camera systems when a marine specimen enters the camera's field-of-view at a range which is within the camera's depth-of-focus, identified by the term FOVAR systems. Such systems were designed for use in relatively clear water in which there is little suspended material or background objects to cause an extraneous reflected signal that could be interpreted as a "subject" by the system. However, there are a number of situations for which the "clear water" conditions are not satisfied, e.g., a subject near the ocean bottom, a cluttered background, or the presence of nearly stationary objects, e.g., suspended particles, plankton, etc., within the field-of-view. For such situations, further improvements are needed for the FOVAR systems.